Versatile objective lens with adjustable correction for different wavelengths and substrate thicknesses for testing optical disks

A typical aspheric singlet used as the objective lens in optical-disk data-storage systems will not work at different wavelengths or with different substrate thicknesses because of spherochromatism. Using two microscope objectives with adjustable collars and a pair of relay lenses, we have constructed a system in which a diffraction-limited spot of any wavelength in the range of 0.4-0.7 mu m can be moved by as much as +/-100 mu m in both the focusing and tracking directions. We accomplished this by simply moving an aspheric singlet mounted in an off-the-shelf optical head. The system uses the adjustable collars of the microscope objectives to correct for the spherochromatism of the singlet and to accommodate the various thicknesses of the substrates. (C) 1997 Optical Society of America.